1. Field of the Invention
The present invention relates to a technology for generating exposure data to expose a resist film formed on a multi-layered semiconductor substrate by a charged particle beam.
2. Description of the Related Art
Lately, in the manufacture of semiconductor devices, such as a large-scale integrated circuit (LSI) and the like, it is desired to form a very fine pattern. Thus, currently a charged particle beam is usually used for pattern generation exposure. It is common to use an electron for a charged particle.
By charged particle beam exposure, a part of charged particles inputted to a resist film is forward-scattered, a part of the particles that have transmitted the resist film are backward-scattered and it is inputted the resist film again. Thus, even when a charged particle beam is inputted to one point on the resist film, an area exposed by the charged particle is not only one point, but it also covers its neighborhood (proximity effect). Therefore, exposure data indicating the exposure pattern of a charged particle beam is usually formed by applying proximity effect correction to layout data indicating a pattern to be formed on the resist film in order to optimize the amount of exposure or dimensions of an exposure pattern (Japanese Patent Application Nos. 2005-101501, 2003-149784 and H11-8187).
With the recent fine semiconductor devices, the form of an exposure pattern for expose a semiconductor substrate has become fine and also its multi-layer structure has become complex. The backward scatter intensity of exposure to such a semiconductor substrate can be calculated with high accuracy by simulation based on a physical model (for example, simulation by a Monte Carlo method). However, actually it takes a very long time to calculate the intensity. Thus, it is desired to calculate the intensity in a shorter time while realizing higher accuracy.
As publicly known, the scatter of a charged particle varies depending on its material. In the prior art disclosed by Japanese Patent Application No. 2005-101501 (hereinafter “patent reference 1”), scatter distribution depending on a distance is prepared as a coefficient a and the backward scatter intensity of each area is calculated by an area density method. If intensity in an area (i, j) is expressed Fbi, j, the Fbi, j is finally calculated as follows.
                              Fb                      i            ,            j                          =                              ∑            l                    ⁢                                    ∑              m                        ⁢                                                                                E                                          n                      -                      1                                                        ⁡                                      (                                                                  i                        +                        l                                            ,                                                                        j                          +                          m                                                ;                        i                                            ,                      j                                        )                                                  ·                                  α                                                            i                      +                      l                                        ,                                          j                      +                      m                                                                                  ⁢                              Q                                                      i                    +                    l                                    ,                                      j                    +                    m                                                                                                          (        1        )            
In the above equation, αi+1, j+m, Qi+1, j+m and En−1 (i+1, j+1; i, j) represent pattern density in an area (i+1, j+m), the amount of exposure applied to an area (i+1, j+m) and a charged particle intensity coefficient indicating the degree of influence on an area (i+1, j+m) of the amount of exposure applied to an area (i, j), respectively.
The charged particle intensity coefficient En−1 corresponds to the coefficient a. The coefficient a can be calculated using a reflection coefficient R, which is a ratio indicating the reflection of a charged particle on a layer, and a transmission coefficient T indicating its ratio of transmitting through the layer prepared by each material. Thus, the backward scatter intensity Fbi, j taking the material of each layer into consideration can be calculated to realize high accuracy. This exposure data can also be appropriately generated in high accuracy.
In the manufacture of semiconductor devices, a factor of accuracy degradation due to a multi-layer structure, such as unevenness in thickness of lower layers, due to non-uniformity of chemical machine polish (CMP) or the accuracy error in dimensions of the pattern of a lower layer, sometimes occur. Stored energy distribution to the resist film varies depending on such a factor. Each value of the coefficients R and T varies depending on the occurrence and the degree of such a factor. Thus, an error occurs in the backward scatter intensity Fbi, j which is calculated according to equation (1). The influence of the error has a tendency to increase due to fine semiconductor devices. Therefore, in even wholly appropriate exposure data, an inappropriate point (poor resolution point) is easily detected by exposure verification. Thus, in the generation of exposure data, including exposure verification, it is also important to take such a factor of accuracy degradation into consideration.
In the prior art disclosed by Japanese Patent Application Nos. 2003-149784 and H11-8187, the amount of calculation is reduced by limiting a point for calculating stored energy including backward scatter intensity as an evaluation point.